A power supply system includes a power source, a load device, and a power interface device connecting the electrical power source to the load device. The power source may include a battery, a power grid, a solar photovoltaic cell, an AC generator, and/or an output of front-end power converter. The power interface device may be configured to increase or decrease the voltage of the power source to provide a suitable voltage for the load device. The power interface device may be a boost converter or a buck converter or any other converter. The load device may include a resistive load, a magnetic load, a capacitive load, a heater. In one implementation, the load device may be a low voltage but a high current load device such as, for example, computer central processing unit (CPU). This type of load device may have many load transient conditions.
During a load transient condition, the current of the load device may substantially change within a very short time period. For example, during the transient condition, the current of the load device may increase from 0A to 100A, or decrease from 100A to 0A, in less than one microsecond. These sudden changes in current can create large voltage variation at the load device and can cause the output voltage to swing outside of the regulated operating window of the load device.
To minimize transient variations, in one implementation, a large power capacitor may be added to the output of the power supply system. The capacitor may source or sink the necessary current during the transient condition and therefore reduce voltage variation caused by the load transient. To this end, the output capacitor is useful in supplementing the converter's slowly rising current to meet the increase in current demand from the load device. Similarly, the output capacitor is useful in sinking the current to meet the sudden decrease in current from the load device. Capacitors, however, are expensive and as such may increase cost or size of the system.
In another implementation, the converter may be pushed to run at a higher bandwidth to respond to a load transient quickly. However, a switching mode converter bandwidth is limited by its switching frequency. Therefore, to push the converter to run at the higher bandwidth, the converter has to operate at a higher switching frequency. This means more power loss because each time there is a turn on/off of the switch, there is a power loss. As such, the power supply system is also limited by the power loss of the power converter placed between the power source and the load device.
Hence, a need exists for a power supply system capable of providing a fast response to the transient condition of the load device while increasing the efficiency and reducing costs and size.